In his free time, Bell experimented with sound waves and became convinced that it would be possible to transmit speech over a telegraph-like system. He enlisted the aid of a gifted mechanic, Thomas Watson, and together the two spent countless nights trying to convert Bell’s ideas into practical form. In 1875, while working on his multiple harmonic telegraph, Bell developed the basic ideas for the telephone. He designed a device to transmit speech vibrations electrically between two receivers and in June 1875 tested his invention. No intelligible words were transmitted, but sounds resembling human speech were heard at the receiving end.On February 14, 1876, he filed a U.S. patent application for his telephone. Just a few hours later, another American inventor, Elisha Gray, filed a caveat with the U.S. Patent Office about his intent to seek a similar patent on a telephone transmitter and receiver. Bell filed first, so on March 7 he was awarded U.S. patent 174,465, which granted him ownership over both his telephone instruments and the concept of a telephone system.
Three days later, on March 10, Bell successfully tested his telephone for the first time in his Boston home. In May, he publicly demonstrated the invention before the American Academy of Arts and Sciences in Boston, and in June at the Centennial Exposition in Philadelphia. In October, he successfully tested his telephone over a two-mile distance between Boston and Cambridgeport.
Alexander Graham Bell continued his experiments in communication, inventing the photophone, which transmitted speech by light rays, and the graphophone, which recorded sound. He continued to work with the deaf, including the educator Helen Keller, and used the royalties from his inventions to finance several organizations dedicated to the oral education of the deaf. He later served as president of the National Geographic Society. Beginning in 1895, he experimented with the possibility of flight and built giant man-carrying kites and a hydrofoil craft. He died in 1922 at his summer home and laboratory on Cape Breton Island, Canada.